Cassini uld provide breakthrough in hunt for Planet Nine ()

Scientists working with data captured by Nasa's Cassini spacecraft have identified a region of the Solar System that they say is most likely to conceal Planet Nine.

Matthew J. Holman and Matthew J. Payne of the Harvard-Smithsonian Center for Astrophysics analysed data recorded by Cassini about its relative position to ground stations on the Earth during its investigation of Saturn. These figures were then used to model the likelihood of a potential ninth planet existing in a wide range of different positions.

Speaking to New Scientist, Payne said that "we put Planet Nine at a whole different slew of locations – all different possibilities on the sky, different distances, different masses – and tried to find out whether that constrains things even more."

The research indicates that the most probable location for Planet Nine is towards the constellation of Cetus, in a patch sky with a 20-degree radius near Aires and Pisces, centred at the celestial coordinates right ascension 40◦, declination -15◦.

Their work follows findings put forward by Agnès Fienga and her team at the Côte d’Azur Observatory in France, which indicated that long-term positional data from Cassini could help to establish a likely area for a ninth planet if the craft is able to operate until 2020. The data is also revealing fine details about of the orbital paths of Saturn, Jupiter, Uranus and Neptune,

However, Nasa notes that "Cassini's mission is planned to end in late 2017, when the spacecraft – too low on fuel to continue on a longer mission – will plunge into Saturn's atmosphere." Some reports added an element of confusion by claiming that the mystery planet was affecting Cassini's orbit, rather than those of other bodies, a claim that Nasa had to debunk.

Planet Nine is thought to exist somewhere within the Kuiper Belt – a ring of rocky asteroids and dwarf planets that extends from Neptune's orbit to beyond dwarf planet Pluto. Evidence for its existence was put forward in a paper published earlier this year by Konstantin Batygin and Michael E. Brown, the latter of whom was largely responsible for Pluto being demoted to dwarf planet through his discovery of Eris.

Holman and Payne used Fienga et al's INPOP model for calculating positional data on the orbits of planets and other bodies before cross-referencing their results with Batygin and Brown’s favoured orbital path for a ninth planet.

The existence of a hypothetical Planet X in the outer solar system has been posited by scientists since the 18th century, leading to the discovery of Uranus, Neptune and Pluto. But it's only since 2014, when astronomers Chad Trujillo and Scott Sheppard observed unusual orbital behaviours in Kuiper Belt objects, that there's been serious evidence for a full-sized planet beyond Pluto.